David Cameron yesterday demanded that Gordon Brown apologise to the House of Commons for allegedly misleading MPs when the prime minister said that a majority of drivers would benefit from a new green car tax.

As Labour MPs warned of a new rebellion against the increases in taxes on gas-guzzling vehicles, Cameron accused the prime minister of breaking the ministerial code after he refused to apologise for "wrong" comments on the tax.

The row erupted after new figures from the Treasury, released on Wednesday, showed that 43% of motorists would be worse off when the new tax takes effect in April 2010. At the moment it costs a maximum of £210 to tax a vehicle registered between March 2001 and March 2006.

In an attempt to encourage people to drive environmentally-friendly cars, the government will increase the tax to £455 in April 2010 for gas-guzzling cars, a rise of £245. Cars with smaller engines will face more modest increases.

In all, 9.4 million of Britain's 21.9 million motorists - 43% - will pay more when the new tax takes effect in 2010. A further 8.4 million (39%) will face the same tax, while 4.1 million (18%) will be better off.

The Tories intensified the pressure on the government last night by releasing new figures which showed that poorer people will be badly hit by the tax change. Of the 9.4 million drivers who will face a higher charge 400,000 are families earning less than £15,000 a year.

Cameron said the Treasury figures showed the prime minister had been wrong when he told the Commons last month that most motorists would be better off as a result of the changes. Brown told MPs on June 4: "The majority of drivers will benefit from it."

Responding yesterday to the prime minister's Commons statement on the G8 summit in Japan, the Tory leader asked: "Will he at least admit that when he told me from the dispatch box that a majority of drivers would benefit, he was wrong? Will he now correct himself and apologise to the house for getting it wrong?"

Downing Street said the prime minister had done nothing wrong because he had spelt out the impact of the tax change in full in the Commons on May 14. Brown had then said: "The majority of motorists benefit or pay no more in vehicle excise duty as a result."

George Osborne challenged the Chancellor, Alistair Darling, yesterday at the monthly session of Treasury questions in the Commons. "Everyone knows that the Labour party is sleepwalking into another 10p tax fiasco," the shadow chancellor said, referring to the government's U-turn over the abolition of the 10p tax rate.

Angela Eagle, the Treasury minister, said that poorer people would be hit. But she told Radio 4's PM programme: "It is important to remember that 50% of people on low income don't drive a car at all."

Ronnie Campbell, the Labour MP for Blyth Valley who tabled a Commons motion signed by almost 50 Labour MPs demanding a rethink, reminded the government that the chancellor had said he would look at the tax again in his autumn pre-budget report. "We're flexing our muscles and saying 'Come on, be careful here. You're going to tax these people, they're working class people, they're our core vote'," he told the BBC.

The government is widely expected to abandon one key element of the tax change within the next year, the retrospective element which means that it applies to cars bought since 2001. But Darling wants to delay an announcement until the last moment to avoid more damaging headlines, after he borrowed £2.7bn to solve the 10p tax row.